Buble told the magazine he had initally called Witherspoon to talk about doing a duet for his new album.

"I had just found out [we were expecting]. It was the greatest day of my life, so I just said, 'You know, I'm having a baby!' And Reese was so sweet about it and excited for me," he said. "It was nice for us to bond that way. I told her before anyone else in the world knew, even members of my own family!"

Witherspoon did end up collaborating with Buble on the duet "Something Stupid" for the singer's upcoming album "To Be Loved," due out on April 23.

Witherspoon previously sang for the film "Walk The Line," where she played June Carter Cash. She won an Oscar for the role.